Hydraulic brake booster



March l10, 1942. B. sTELzER HYDRAULIC BRAKE BOOSTER Filed June 13, 19414 YIIIIIIIIIIII(II.

Patented Mar, 10, 1942 UNITED STATES PATENT OFFICE HYDRAULIC BRAKEBOOSTER Berteli Stelzer, St. Petersburg, Fla., assigner t WilliamSteller, Detrolt,'Mich.

Application June 13, 1941, Serial No. 397,889

7 Claims.

The invention relates to hydraulic brake boosters, and more particularlyto a brake booster where a primary pressure is produced with aconventional master cylinder operated by the operator, and the primarypressure thus produced is used, together with the help of a poweroperated expansible motor mechanism, to produce a secondary pressure,and where the mechanical forces which produce the secondary pressure areused togovern the amount of power applied to obtain a boosted hydraulicpressure which is in proportion to the manual effort. The invention issomewhat related to the disclosures shown in the` followingapplications: Ser. No. 281,375 led June 27, 1939; Ser. No. 308,367 filedDecember 9, 1939; Ser. No. 303,837 filed November 10, 1939.

The object of the invention is to produce a novel booster which may bemounted anywhere on the vehicle independent of the'brake pedal or mastercylinder location, and where all external mechanical operatingconnections as well as hydraulic or air pressure control cylinders areeliminated.

Another object is to simplify the construction so that conventionalmaster cylinder seals may be used, and` this is made possible by a novelprinciple where the mechanical forces transmitted to the secondarycylinder are used to control the power applied to the booster, so thatthe hydraulic pressure in the wheel cylinders is apredeterminedpmultiple of the hydraulic pressure in the master cylinder,in order to have the feel of the brakes. l s f A further aim is toobtain a novel construction that lends itself to a simplification indesign where the booster is a self-contained'unit and where the numberof parts may be reduced to a minimum.

Other advantages will appear by inspection of the drawing, wherein: f

Fig. 1 is a cross section through the booster connected to aconventional braking system which is shown diagrammatically;

Fig. 2, a detail view of the balancing lever means, carried out as adisc with radial slots to facilitate dishing:

Fig. 3, a modication of the construction shown in Fig. 1, where insteadof the disc illustrated in Fig. 2 a plurality of balancing levers isused;

Fig. 4,l a fractional view showing a cross section through the valvemechanism as in Fig. 1, ex-

' ceptthat it is in the open position where the valve means direct powerto the expansible motor mechanism; and

Fig. 5, a diagram to illustrate the principle of the invention.

Describing the invention now more in detail,

unit, having a primary or low pressure cylinder 5, a secondary or highpressure cylinder 6, and a power cylinder l, which are co-axial andsecured together to form one rigid piece to house the pistons, valvemeans, and other elements that are required for the proper function ofthe `valve plunger 20, which' latter booster. The primary cylinder 5,which has a flange 8 to form an end plate for the power cylinder 1, isadapted to receive a piston 9 equipped with a piston seal I0 and havinga shoulder to engage the balancing disc II. This disc is shown more indetail in Fig. 2 and performs the same function as a plurality of leversas shown in Fig. 3. It has radial slots I2 and I2 which reduce theresistance to dishing of the disc. The annular surface near the outerperiphery of the disc II is in contact with a ring I3 which is securedto the power piston I4 adapted to move in the power cylinder l. Thispower piston I4 is provided witha piston seal I5, and has a central borethrough which the piston I6 may slide, whereby seal II serves to preventthe passage of air. One end of the piston I6 is provided with ahydraulic seal I8 to slide in the secondary cylinder 6 and is urged intothe oil position, as shown in Fig; 1, by a coil spring I9. The oppositeend of piston I6 is adapted to house a slidable valve plunger 2U havinga central bore in communication with the vacuum chamber 2I throughpassage 22. room for the guide pin 23 extending from the primary piston9 and slidably centering inthe secondary piston I 6 at 24. The valveplunger 20 is retained by a circular plate 25 whose central portion isprovided with a thread engaging the piston Ii and serves as a valve seatfor the is urged against it by means of a coil spring 26. The disc orplate 25 has an annular bead 21 contacting disc or lever plate II,whereby the point of contact is the center of the fulerum of the lever.The plate II may be considered as an innite number of levers. each ofwhich has one end in contact This bore also provides` cylinder, I useasource of fluid pressure.

with piston 9 and the other end with the power piston I4 through themedium of ring I3, and

an intermediate point is in contact with the secondary piston I6 throughthe medium oi plate 25, whereby the intermediate point of contact is online 28, Fig. 2..` The piston 9 has a conical surface 29 which serves asa valve head to seat in the bore of the valve plunger 20. In the offposition the valve head 29 leaves the passage open so that there is alowpressure or vacuum in chamber 39 as well as in chamberll, i. e., onboth sides of the power cylinder piston. .In order to control theopening of the vacuum valve 29 I provide adjustable stop screws 3|vwhich control `the location of the power piston I4 in thel oiT'position. The retractable movement of the` primary piston, and with itthe valve head 28 is limited by an extension 32 whichV serves to crackopen check valve 33 against a stop 34. The ball the vacuum produced inthe intake manifold of, an internal combustion engine. In such anapplication thepressure connection of the booster trate the principle ofthe invention. 50 denotes the primary cylinder, i 'the secondarycylinder,

f and 52 the power cylinder, which are all in fixed relation. 53 denotesthe balancing means or lever, and 54 the valve. The pivot point 55 isrepresentative-of. line 28 or pivot point 45. It is apparent that arelative movement between the piston in the primary cylinder 50 and thepiston in the power cylinder causes operation of the valve 54.

Describing now the peration ofthe novel braking system, it is assumedthat the booster is `in the o if position, `as shown in Fig. 1. Tosimplify the description, I divide the hydraulic circuit of the systeminto a primary circuit or low pressurecircuit, and a secondary circuitor high pressure circuit. The primary circuit consists of the hydraulicfluid put under pressure directly by the master cylinder, or comprisingthe master cylinder, line 3, and chamber 48 of the primary cylinder, andthe secondary circuit consists of the hydraulic fluid put under pressureby the booster mechanism, or comprising chamber 49 of the secondarycylinder, line 4, and wheel cylinders 2.

kAssuming-that the primary and the secondary circuits are completelyfilled with brake fluid, and that the operator now depresses thebrakepedal to apply the4 brakes,fa hydraulic pressure is produced in themaster cylinder which is communicated through line 3 to chamber 48, andthrough the open check valve 33 and line 3 6 to chamber 49 and the Wheelcylinders 2 which would be open to the atmosphere through. an

air cleaner 31. The atmospheric pressure is communicated to chamber 38through the medium of a flexible hose 39. The low pressure side. whichis chamber 2l, would be connected to the intake"` manifold or othersource of vacuum or suction through tube 4I and check valve 42. Thepurpose of the latter is *to* prevent air or gas from entering intochamber 2l.Vv wherebythe latter serves as a reservoir lso that `severalbrake applications can be made even though the engine is not inoperation.V In principle, the chamber 3 8 is connectedto a source oflower pressure. Thus 3l may representa source of higher pressure such asan `air pump; or a supply of compressed gases, and chamber 2l may thenbe open to the atmosphere, whereby 40 would represent an air cleaner.`

In order to prevent piston seal I0 from coming into .contact with a drycylinder wall during operation, which would destroy it in a short time,I provide a packing 43,- preferably of feit satu- .rated with brakefluid', 'in `a groove provided inl piston 9. This precaution is notnecessary in the secondary piston, because in operation the piston movestowards a wetted surface.

In the modified construction shown in 3 i the balancing disc Il isreplaced by a plurality of balancing levers 44 pivoted at 45 on pinswhich 4 illustration an arrangement of four is intended.

One ofthe levers may be 'considered hidden behind primary piston 9. i

l In Fig. 5 I show the major-elements diagrammatically in a fundamentalarrangement Vto illusare supported on brackets or bosses 46 extendingfrom plate 41 whichtakes the place of plate B.

thereby expand tov engage the brake shoes with the brake drums. Thus theheight of the primary pressure level and that of the secondaryv pressurelevel are yet the same. The effort to expand the'brake shoes until theycome in contact with .the drums is comparatively small; therefore, the

hydraulic pressure'isyet at a low level.` How-` ever', it may bevsufllcierit to move piston 9 until the valve head 29 seats on plunger20, but spring 25 is of suicient strength to resist further movement.This valve action as yet has no eiect on the operation of the expansible'motor mechanism. 'Ihe work required to expand the brake shoes isperformed .solely by manual effort. The

hydraulic fluid is still able to flow from the master cylinder to thewheel cylinders as the check valve permits flow in this direction even-thoughextension 3 2 is releasedfrom the ball.

After the brake `shoes come into contact with the brake drums, and theoperator depresses the foot pedal further,the resistance, and with itthe hydraulic pressure, increases; spring' 26 thereby yields and.permits opening of the valve which directs power to the expansible motormechanism, i. e., plunger 20 is unseated from plate 25, allowing air topass from the atmosphere through hose connection 39, chamber 38, intochamber 38 to move the power piston, as shown in Fig. 4. Before thishappens, or while the valve vis being opened, disc ll is being dishedsimilarly The outer periphery;

to a Belleville washer. of the balancing disc H remains stationary be-"cause piston I4 rests agains'I stop'screws 3i;

therefore, piston IB is moved in the same direc-A tion as piston 9, onlya smaller distance. vThe ratio of this movement is the same as thebooster ratio, which is equal to theradial distance on disc Il betweenthe point of contact of piston 9 and that of ring I3 divided by theradial distance l between line 28 and thepoint ofcontact of ring .In theembodiment shown the booster ratio is approximately 1:3, and should varyaccording example) one-third of `the work and the ex-v pansible motormechanism is doing two-thirds.v The pressure in the secondary, circuitis now piston and are therefore opposed by the reaction of the latter.This may be best understood by inspection of Fig. 5. It is apparent thatthe various mechanical forces are in a pre-determined relation to eachother, 'I'he proportion of the force produced by the piston in theprimary cylinder 50 to that of the piston in the power cylinder 52depends on "the length of the lever three times that in the primarycircuit, and

check valve 33 is closed. The action oi.' the balancing disc Il is tomaintain the proportion of the primary pressure to the secondarypressure by regulating the supply of power to the expansible motormechanism by means of the valves. Thus as soon as enough air has beenadmitted to chamber 30, and pistons 9 and I4 are therefore balanced (theopposing forces of piston 9 and piston Il acting on iulcrum point 21balancing each other so that one opposes, but not overpowers the other),spring 26 immediately closes the valve 20, causing a relative movementbetween piston 9 and piston I6 by pushing piston 9 away from piston I9until valve 29 is seated on 25 and shuts olf the further supply of air.If too much air has been directed to chamber 39, piston I4 overpowerspiston 9, causing piston 9 to move away from piston I6 whereby valve 20is seated on 25; valve head 29 unseats; and air is permitted to escapefrom chamber through the central bore of plunger 20 into chamber 2l, andfrom there into the intake manifold 40 or other source of low pressure,until the equilibrium is established again.

Upon the retractile movement of the brake pedal, when the operatorreleases it, the pressure in the primary circuit drops suddenly,`and theprimary piston 9 is overpowered immediately, causing it to move awayfrom piston I6 whereby valve 29 unseats and plunger 20 is closed so thatthe air in chamber 90 is allowed to escape into chamber 2l until thepressures on both sides of the power piston Il are equalized and thepistons I6, 9, and I4 are allowed to return to the oi position, urged byspring I9 and the hydraulic pressure in the secondary circuit. In theoff" position the check valve 33 is cracked open again by extension 32and the hydraulic uid is permitted to return to the master cylinder,whereby the same hydraulic pressure exists again in thel primary and inthe secondary circuit.

The construction shown on the drawing was designed primarily toillustrate the principle of the invention and to show the necessaryelements in one form, there being a primary cylinder 5 which convertsthe primary hydraulic pressure of the master cylinder into a mechanicalforce, an expansible motor mechanism or power means 'consisting of acylinder 1 and a piston Il to produce a mechanical force to boost the`secondary hydraulic pressure, a secondary cylinder 6 using themechanical force produced by the primary cylinder and the mechanicalforce produced by the expansible motor mechanism to produce a secondarypressure to operate the wheel cylinders 2, valve means consisting of aplunger 20, a seat on disc 25, and a valve head 29 to direct power toand from the expanslble motor mechanism, and balancing means, orbalancing levers Il or 44 responsive to' the mechanical forces producedby the hydraulic pistons 9 and I6 and the power piston Il. Obviously,the mechanical forces produced by the primary piston and the powercylinder piston act in unison to move the secondary arms of thebalancing beam 53, and the reaction of the piston in the vsecondarycylinder 5l is ciples involved are susceptible to numerous other iapplications which will readily occur to persons skilled in the art;therefore, I do not wish to be limited to the shown embodiments orotherwise than by the terms of the appended claims.

I claim:

1. In a hydraulic braking system for an automotive vehicle having wheelcylinders to apply the brakes, a master cylinder operated by theoperator to produce a primary pressure, a hydraulic booster, saidbooster having a primary hydraulic cylinder withV a piston thereinresponsive to the hydraulic pressure in said master cylinder, and asecondary cylinder with a piston therein .to produce a secondaryhydraulic pressure for the wheel cylinders, means to transmit themechanical reaction force of the piston in the primary cylinder to thepiston in the secondary cylinder to produce a hydraulic pressure in saidsecondary cylinder, an expansible motor"mech anism adapted to act onsaid piston in said secondary cylinder to increase the hydraulicpressure therein, a source of power to operate said expansible motormechanism, valve means responsive to the mechanical `force transmittedfrom the piston in said primary cylinder to the piston in said secondarycylinder, and to the mechanical force transmitted from said expansiblemotor mechanism to said secondary piston to direct power to saidexpansible motor mechanism to boost the secondary pressure in apre-determined proportionvto the primary pressure, fluid pressuretransmitting means from said master cylinder to said primary cylinderand from said secondary cylinder to said wheel cylinders; and fluidpressure transmitting means between said primary cylinder and saidsecondary cylinder with means interposed to prevent passage of iiuidfrom said secondary cylinder to said primary cylinder except in the offposition.

2. In a hydraulic braking system for an automotive vehicle having wheelcylinders to apply the brakes, a master cylinder operated vby theoperator, a hydraulic brake booster having a primary hydraulic cylinderin communication with said master cylinder and a secondary hydrauliccylinder in communication with said wheel cylinders, pistons in' saidcylinders, an expansible motor mechanism adapted to exert a force on thepiston in said secondary cylinder, a source of power to operate saidexpansible motor mechanism, said piston in said primary .cylinder beingadapted to convert the hydraulic pressureinto a mechanical force, meansto transmit the latter to the piston in said secondary cylinder, valvemeans responsive to said mechanical force produced by the piston in saidprimary cylinder and the force produced by said expansible motormechanism to direct power to said expansible motor mechanism tooperatethe latter to boost the wheel cylinder hydraulic pressure to apredetermined multiple of the master cylinder hy draulic pressure, and-fluid transmitting means between said primary cylinder and saidsecondary cylinder to establish communication when said booster is inthe off position.

3. In ahydraulic braking system for an' automotive vehicle having wheelcylinders to apply the brakes, amaster cylinder'operated by the operatorto produce a primary pressure, a hydraulic brake booster having aprimary hydraulic y cylinder in communication with saidl mastercylinder,l and a secondary hydraulic cylinder in communication with saidWheel cylinders to produce a secondary pressure, a piston in saidsecondary cylinder, a piston in said primary cylinder, an expansiblemotor mechanism arranged to l act on said piston in said secondarycylinder to boost the secondary hydraulic pressure, mechanical pressuretransmitting means to transmit the force produced by the primaryhydraulic pressure on the piston in said primary cylinder to the pistonin said secondaryrcylinder to boost the secondary hydraulic pressure,valve means draulic .comnunication between said primary pressure andsaid secondary pressure whensaid booster is in the ofi" position.

, 4. In a hydraulic braking system for a vehicle having wheel cylindersto apply the brakes, a`

master cylinder operated by the operator to pro-Y duce a primarypressure, a `hydraulic, brake booster having a primary hydrauliccylinder in communication with said master cylinder, and a secondaryhydraulic cylinder in communication with said wheel cylinders to producea secondary pressure, a piston in said primary cylinder. a piston insaid secondary cylinder, an expansible motor mechanism, a source ofpower for said expansible motor mechanism balancingA lever means on theprinciple of a lever on one end of which the primary cylinder piston isacting and on the Aother end of which said expansible motor mechanism isacting, and wherebyk the ,fulc'rum at an intermediate position acts on`said seconde. ary cylinder piston so that the combined forces` valvemeans 'to cause `said `expansible motor mechanism to reduce its effort,and whereby an excursion caused by the yielding of said expansibie motormechanism urges said valve means` to cause said expansible motormechanism to iny crease its effort, in order to produce a secondarypressure which is a pre-determined multiple of the primary pressure, andmeans to establish` communication between said secondaryl pressure andsaid primary pressure when said booster is in the ofi position.

5. The construction as` claimed in claim 2 where said hydraulic brakebooster, said expansible motor mechanism, said means to transmit themechanical force to the secondary cylinder piston, and said valve means,form a single, selfcontained unit, connected to the rest of the brak ingsystem with fluid pressure lines. 4 l

6. The construction as claimed in claim 4, where said lever meansconsists'of a disc periorated radially to facilitate dishing, where thesurface near the periphery is in contact with the power means, and thesurface near the center of said disc is engaged by said 'primary piston.

7. The construction as claimed in claim 4,

-where said lever means consists of a discwhcre the surface near theperiphery is in contact with the power means, and the surface near thecenter of said discis engaged by-said primary piston. BERTELI sTaLzER

